[Mesa-dev] Interest in GL_ARB_gl_spirv support?

[Matt Turner]

On Tue, Jul 26, 2016 at 9:16 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Tue, Jul 26, 2016 at 4:50 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>
>> On Tue, Jul 26, 2016 at 7:44 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> > On Wed, Jul 27, 2016 at 12:29 AM, oscar bg <rtfss1 at gmail.com> wrote:
>> >> Hi,
>> >> seems this year 2016 OpenGL ARB update brings a small number of
>> >> extensions..
>> >> seems the most important is GL_ARB_gl_spirv.. seems like SPIRV as a
>> >> binary
>> >> format for OpenGL and Mesa doesn't have any binary format even
>> >> supporting
>> >> ARB_program_binary ext.. a Nvidia driver is already providing support
>> >> from
>> >> day 1 for Linux as always..
>> >>
>> >> just asking how difficult would be to bring support to Mesa drivers..
>> >> and if
>> >> there is any interest by Mesa devs start working on it soon..
>> >>
>> >> seems already we have SPIRV support in Mesa in Vulkan drivers: Anvil
>> >> Vulkan
>> >> Intel driver and some days ago RADV a open source Vulkan driver for AMD
>> >> GPUs
>> >> has been anounced.. as this drivers already eat SPIRV code seems this
>> >> extension would take less work to port to this two vendor GPUs?
>
>
> We're thinking about it but, unfortunately, I haven't had much time to look
> into the extension.  One thing that I can say right now, is that the
> spirv_to_nir pass isn't what you'd call OpenGL-friendly.  If you pass it
> invalid SPIR-V, it will crash.  What little error checking it does do is
> done via asserts.  That's perfectly acceptable in the Vulkan world but
> unless they went out of their way to ok it in the extension, crashing
> generally isn't acceptable in OpenGL.  Also, it's not entirely clear what
> all hoops we would have to go through to tie a NIR shader into the OpenGL
> state upload paths for things like uniforms, inputs/outputs, etc.  This
> isn't to say that it can't be done but it's substantially more than zero
> work.

The spec says

    The OpenGL API expects the SPIR-V module to have already been validated,
    and can return an error if it discovers anything invalid in
    the module.  An invalid SPIR-V module is allowed to result in undefined
    behavior.